Ignition device for an internal combustion engine

ABSTRACT

An ignition device for an internal combustion engine comprises a preselector stage and an output stage for controlling the flow of current through the primary winding of an ignition transformer. The ignition device is particularly suited for an externally ignited internal combustion engine. The output stage comprises a pnp-transistor having its collector terminal directly coupled to a ground connection of the ignition device to improve proper loss dissipation. A decoupling device is coupled between the preselector stage and the output stage, and is provided to protect the preselector stage by decoupling it from the output stage.

FIELD OF THE INVENTION

The present invention relates to ignition devices for internalcombustion engines and, in particular, to ignition devices employingtransistors in the output stages thereof.

BACKGROUND INFORMATION

An ignition device for an internal combustion engine is shown in GermanPatent No. 28 25 830. The ignition device uses a pnp-transistor in itsoutput stage. The primary winding of an ignition transformer is coupledto the collector terminal of the transistor. The emitter terminal of thetransistor is coupled to ground by a current measuring resistor. Duringthe operation of the ignition device, there are high power losses at theoutput stage, which are removed from the collector terminal to a heatsink. However, the collector terminal must also be electricallyinsulated from the heat sink when a square-shaped voltage appears duringthe shut-down process. These opposing requirements have been fulfilledby using an electrically-insulating ceramic layer having good thermalconductivity located between the collector terminal and the heat sink.One problem with the ceramic layer, however, is that it makes theassembly of the ignition device considerably more expensive and oftendoes not compensate for the alternating thermal stresses occurringparticularly in high power ignition devices.

Ignition devices are also shown in French Patent Nos. 2,407,363 and2,318,323, U.S. Pat. Nos. 3,945,362 and 4,106,462, and German Patent No.3,231,125, wherein the emitter terminals of the transistors in theoutput stages are coupled to ground connections.

SUMMARY OF THE INVENTION

The present invention is directed to an ignition device for an internalcombustion engine. The ignition device comprises an ignition transformerincluding a primary winding and a secondary winding. A direct currentsource is coupled to the primary winding for supplying electric currentthereto. First means are coupled to the primary winding for controllingthe flow of electric current therethrough. The first means includes apreselector stage and an output stage. The output stage includes a firsttransistor having a first conductivity. The collector terminal of thefirst transistor is directly coupled to a ground connection of theignition device.

The ignition device further comprises second means coupled between thepreselector stage and the output stage for decoupling the output stagefrom the preselector stage and preventing the uncontrolled starting ofthe output stage. The second means includes a second transistor. Thecollector terminal thereof is coupled to the base terminal to the firsttransistor; the emitter terminal thereof is coupled to the emitterterminal of the first transistor; and the base terminal thereof iscoupled to the positive terminal of the direct current source. Thesecond means further includes a first resistor coupled between the baseterminal of the second transistor and the positive terminal of thedirect current source.

In one ignition device of the present invention, the second meansfurther includes a third transistor having a second conductivity. Thecollector terminal of the third transistor is coupled to the baseterminal of the first transistor. The emitter terminal of the thirdtransistor is coupled to a ground connection of the ignition device. Thepreselector stage is coupled to the base terminal of the thirdtransistor to control that transistor.

In another ignition device of the present invention, the output stagefurther includes an electric current measuring device coupled to theprimary winding and to the preselector stage. The current measuringdevice measures the electric current flowing through the primarywinding. It in turn transmits signals indicative thereof to thepreselector stage. The current measuring device includes a secondresistor coupled to the primary winding and to the preselector stage.The second resistor transmits signals to the preselector stageindicative of the voltage drop across the primary winding.

One ignition device of the present invention further comprises a thirdresistor coupled between one terminal of the second resistor and aninput terminal of the preselector stage. The third resistor exhibits ahigher resistivity than the second resistor. A fourth resistor iscoupled between the other terminal of the second resistor and anotherinput terminal of the preselector stage. The fourth resistor exhibits ahigher resistivity than the second resistor. A first zener diode iscoupled between the third resistor and the respective input terminal ofthe preselector stage, and is coupled to ground. A second zener diode iscoupled between the fourth resistor and the respective input terminal ofthe preselector stage, and is coupled to ground. The first and secondzener diodes thus protect the respective input terminals of thepreselector stage.

In another ignition device of the present invention, the preselectorstage includes a fourth transistor and a diode. The anode terminal ofthe diode is coupled to the emitter terminal of the fourth transistor.The cathode terminal of the diode is coupled to the base terminal of thefirst transistor and to a ground connection of the ignition device. Afifth transistor is coupled between the cathode terminal of the diodeand the ground connection. The diode is provided to protect thereselector stage from voltage peaks across the primary winding.

In another ignition device of the present invention, the second resistoris coupled between the emitter terminal of the first transistor and theground-side terminal of the primary winding. The ignition device furtherincludes a fifth transistor. The emitter terminal of the fifthtransistor is coupled to the ground-side terminal of the primarywinding. The collector terminal thereof is coupled to the base terminalof the first transistor. A voltage divider is coupled between theemitter and collector terminals of the fifth transistor. The baseterminal of the fifth transistor is in turn coupled to the pick-off ofthe voltage divider.

One advantage of the ignition device of the present invention is that byusing a pnp-transistor in the output stage of the ignition device and bycoupling its collector terminal to the ground connection of the device,which has good thermal and electrical conductivity, large power lossescan be dissipated with operational reliability. Moreover, without aninsulating layer between the collector terminal and the groundconnection, the assembly of the ignition device is simplified andthereby made less expensive. Another advantage is that a predominantpart of the ignition device can be integrated monolithically in aparticularly advantageous manner, whereby small variances in theimportant electrical characteristic values of the device can be achievedwith large scale production.

Other advantages of the device of the present invention will becomeapparent in view of the following detailed description and drawingstaken in connection therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an ignition device embodying thepresent invention.

FIG. 2 is a partial schematic illustration of an ignition deviceembodying the present invention, showing the output stage and thedecoupling device in further detail.

FIG. 3 is a partial schematic illustration of another embodiment of anignition device embodying the present invention, illustrating the outputstage and the decoupling device thereof.

FIG. 4 is a partial schematic illustration of another ignition deviceembodying the present invention, including means in the output stage forpreventing unintentional re-starting thereof and a decoupling diode inthe preselector stage.

FIG. 5 is a schematic illustration of the output stage of an ignitiondevice embodying the present invention designed with monolithicallyintegrated technology.

FIG. 6 is a partial cross-sectional view of a semiconductor substrateused in the ignition device of the present invention.

DETAILED DESCRIPTION

In FIG. 1, an ignition device embodying the present invention isindicated generally by the reference numeral 3. The ignition device 3 isparticularly suited for an externally ignited internal combustion engine(not shown). The ignition device 3 includes an ignition transformer 1having a primary winding 1a and a secondary winding 1b. Direct currentis supplied to the primary winding 1a from the positive terminal of adirect current source, as shown in FIG. 1.

The ignition device 3 further comprises a current-controlling device forcontrolling the current flowing through the primary winding 1a. Thecurrent-controlling device comprises a preselector stage 3a and anoutput stage 3c. The output stage 3c includes a transistor T100 having afirst type of conductivity. The transistor T100 is preferably apnp-transistor or a pnp-Darlington transistor. The collector terminal ofthe transistor T100 is coupled to a ground connection of the ignitiondevice 3. A decoupling device 3b is coupled between the preselectorstage 3a and the output stage 3c. The decoupling device 3b is providedto decouple the preselector stage 3a from the output stage 3c. It thusprotects the preselector stage 3a from the high square-shaped voltageappearing at the output stage 3c during the shut-down process.

In the embodiment of the present invention shown in FIG. 2, thedecoupling device 3b comprises a transistor T20 having a second type ofconductivity. The collector terminal of the transistor T20 is coupled tothe base terminal of the transistorr T100 in the output stage 3c, andthe emitter terminal is coupled to the ground connection of the ignitiondevice 3. The base terminal of transistor T20 is coupled to andcontrolled by the preselector stage 3a. Since the transistor T100 is apnp-transistor, the decoupling transistor T20 is also a pnp-transistor.The decoupling transistor T20 has at least the same blocking capacity asthe square-shaped voltage appearing at the transistor T100.

In FIG. 3, another embodiment of an ignition device of the presentinvention is illustrated. The decoupling device comprises a transistorT20, having its collector terminal coupled to the base terminal of thetransistor T100 via a resistor R21. The decoupling device furthercomprises another transistor T25, coupled in parallel to theemitter/base junction of the transistor T20. The collector terminal ofthe transistor T25 is coupled to the base terminal of the transistorT20, and the emitter terminal of the transistor T25 is coupled to theground connection of the ignition device. The emitter terminal of thetransistor T20 is also coupled to ground via a resistor R22. Theresistor R22 is a current-detecting resistor. There is a voltage dropacross the resistor R22 when electric current flows through thetransistor T20. As wil be recognized by those skilled in the art, theresistor R22 is a useful control device.

The base terminal of the transistor T25 is located at the pick-off of avoltage divider formed by resistors R23 and R24. The voltage divider iscoupled between the base terminal of the transistor T20 and the groundconnection of the ignition device. The partial resistor R24 is coupledto the ground connection of the ignition device, and is adjustablydesigned to determine the base voltage of the transistor T25. Theadjustment takes place in a particularly advantageous manner by usingauxiliary resistors R31 and R32 coupled in parallel with the resistorR24 and also in series with a zener diode. In the operation of thedevice, if the zener diode is overloaded, it is destroyed, and theauxiliary resistors are then coupled in parallel to the partial resistorR24. Therefore, in the same way that the current buildup for thetransistor T100 is regulated by the transistors T25 and T20, thetransistor T30 and resistors R31, R32 can alternatively regulate theemitter current of the transistor T100.

In FIG. 4, another embodiment of an ignition device of the presentinvention is illustrated. The decoupling device comprises a diode D41.The anode terminal of the diode D41 is coupled to the emitter terminalof a control transistor T40 in the preselector stage. The cathodeterminal of the diode D41 is coupled to the base terminal of thetransistor T100. It is also coupled to the ground connection of theignition device via a load resistor R42. The diode D41 has at least theblocking capacity of the square-shaped voltage appearing at thetransistor T100.

One advantage of the ignition device of the present invention is thatthe transistor T100, mounted with its collector terminal in the outputstage 3c, is coupled in an electrically conductive manner directly tothe ground connection and, therefore, can be directly assembled to aheat sink also coupled to the ground connection. In contrast toconventional ignition devices, the ignition device of the presentinvention facilitates the dissipation of the power loss occurring duringthe operation of the ignition device, since no thermal insulating layersare arranged between the collector terminal of the transistor T100 andthe heat sink.

Another advantage of the ignition device of the present invention isthat its assembly is considerably simplified in comparison to knownignition devices. Therefore, the ignition device of the presentinvention can typically be produced considerably more economically thanconventional ignition devices. To facilitate trouble free operation ofthe ignition device of the present invention, the decoupling device 3bis provided to avoid damaging the preselector stage 3a by the highsquare-shaped voltage appearing during shut-down of the transistor T100.

Another advantage of the ignition device of the present invention isthat the uncontrolled restarting of the transistor T100 is reliablyprevented after a systematic shut-down thereof. This is achieved byemploying an additional transistor T43, as shown FIG. 4. The collectorterminal of the transistor T43 is coupled to the base terminal of thetransistor T100; the emitter terminal thereof is coupled to the emitterterminal of the transistor T100; and the base terminal thereof iscoupled to the positive terminal of the direct current source via aresistor R44. Therefore, the transistor T43 is only activated andswitched by its base terminal when its base terminal has a more negativepotential than its emitter terminal. However, this only occurs when asquare-shaped voltage having a magnitude of about 400 volts appears whenthe transistor T100 is shut-down (which could restart the transistor).

In the embodiments of the ignition device of FIGS. 1 and 4, a resistorR12 is coupled between the positive terminal of the direct currentsupply and the terminal of the primary winding 1a (which is located awayfrom the ground connection) of the ignition transformer 1, to measurethe electric current therethrough. There is a voltage drop across theresistor R12 during the flow of current through the primary winding 1a.The voltage drop, or signal indicative thereof, is transmitted to thepreselector stage 3a for control purposes, as described further below.

In the embodiments of the ignition device of FIGS. 2 and 3, a currentmeasuring resistor R12' is coupled between the emitter terminal of thetransistor T100 and the ground side terminal of the primary winding 1aof the ignition transformer 1. In the ignition device of FIG. 2, thevoltage drop across the measuring resistor R12' is picked-off by tworesistors R13 and R14, having a higher resistivity than the resistorR12', and is transmitted to input terminals of the preselector stage 3a.The input terminals are protected by zener diodes Z1 and Z2 operatingagainst ground. The high voltage appearing at both terminals of themeasuring resistor R12' during the shut-down phase is uncoupled by theresistors R13 and R14, and the zener diodes Z1 and Z2.

In the ignition device of FIG. 3, another transistor T30 is coupled inparallel to the emitter/base junction of the transistor T100 and thecurrent measuring resistor R12'. The emitter terminal of the transistorT30 is in turn coupled to the ground side terminal of the primarywinding 1a of the ignition transformer. The collector terminal of thetransistor T30 is coupled to the base terminal of the transistor T100.And the base terminal of the transistor T30 is coupled to the pick-offof a voltage divider R31, R32 located between its emitter and collectorterminals. As described above in connection with the decouplingtransistor T25, the partial resistor R32 of the voltage divider islocated closer to the ground connection of the ignition device 3 and isadjustably designed.

One advantage of the preselector stage 3a, the output stage 3c, and thedecoupling device 3b of the ignition device 3 is that they can bemanufactured with monolithically integrated technology. As a result,extremely small variances in the important electrical characteristicvalues of the device can be achieved with large scale production. Indesigning the ignition device 3 with integrated technology, the currentmeasuring resistor R12' is mounted as a divided resistor at the emitterregion of the transistor T100. As a result, a uniform currentdistribution is obtained over the entire active emitter area of thetransistor T100. The current measuring resistor R12' and the currentregulating circuit in the output stage of FIG. 3, are integrated intothe emitter/base junction of the pnp-transistor T100. The transistor T30is designed as a lateral pnp-transistor. In the same way, the decouplingdevice of FIG. 3 can be integrated with the transistors T20 and T25.

The transistor T43 in the ignition device of FIG. 4, which preventsuncontrolled restarting of the transistor T100, can likewise beintegrated monolithically as a lateral pnp-transistor into thebase/emitter junction of the transistor T100 mounted in the output stage3c. Both the control stage 3a and the transistors T20, T25, or thedecoupling diode D41 (provided for decoupling purposes), are attached tothe thick layer integrated circuit as separate chips and are coupled tothe rest of the circuit by bonded connections. The resistors R33, R44and R12 are preferably thick-layer film resistors.

FIGS. 5 and 6 illustrate the output stage 3c of the ignition device 3designed to be monolithically integrated. FIG. 5 illustrates the circuitdiagram of the output stage and FIG. 6 is a cross-sectional view of asemiconductor substrate. The output transistor T100 is designed as atwo-stage Darlington transistor including components T101 and T102. Inaccordance with the embodiment of FIG. 4, the transistor T43 isshort-circuit proof and designed as a pnp-lateral transistor. Theintegration of the resistors R50 and R51, as shown in FIG. 5, isachieved in a manner known to those skilled in the art and is thereforenot shown in FIG. 6.

As shown in FIG. 6, the semiconductor substrate includes a highlyresistant, p-conducting substrate 60 into which n-conducting base heatsinks 62, 63 and 64 are diffused therein. Highly doped p-conductingemitter zones 65, 66, 67 and 68 are in turn diffused into the heat sinks62, 63 and 64, respectively. The heat sinks 62 and 63 represent thebases of the transistors T101 and T102 of the Darlington transistor,respectively. The heat sink 64 represents the base heat sink surroundingthe lateral (short-circuit proof) transistor T43. The other sinks 69, 70and 71 are made of n-conducting silicon and are highly doped withphosphorus. The sinks 69, 70 and 71 include low-resistant contacts 612,614 and 617, respectively, on the otherwise highly resistant base heatsinks doped with phosphorus. The highly doped phosphorus layers exert agettering action, which is favorable for both blocking and for theamplification of the transistors T43, T101 and T102.

The external connecting lines 612 to 618 are coupled to each other ashereinafter described. The transistors T101 and T102 are coupled into aDarlington pair by coupling the terminals 613 and 614 together. Theterminal 612 is the external base terminal and the terminal 615 is theexternal emitter terminal of the Darlington transistor. For integratingthe pnp-lateral transistor T43, its lateral collector terminal 618 iscoupled to the base terminal 612 of the Darlington transistor T101,T102. The lateral emitter terminal 616 of the transistor T43 is coupledto the emitter terminal 615 of the Darlington transistor. The transistorconfiguration therefore comprises three external terminal regions: 612(the base of the Darlington transistor), 617 (the base of the lateraltransistor), and 615 (the emitter of the Darlington transistor).

We claim:
 1. An ignition device for an internal combustion engine, comprising:an ignition transformer including a primary winding and a secondary winding; a direct current source coupled to the primary winding for supplying electric current thereto; first means coupled to the primary winding for controlling the flow of electric current therethrough, the first means including a control stage and an output stage, the output stage including a first transistor having a first conductivity, the collector terminal of the first transistor being directly coupled to a ground connection of the ignition device; second means coupled between the control stage and the output stage for decoupling the output stage from the control stage and preventing the uncontrolled starting of the output stage, the second means including a second transistor, the collector terminal thereof being coupled to the base terminal of the first transistor, the emitter terminal thereof being coupled to the emitter terminal of the first transistor, and the base terminal thereof being coupled to the positive terminal of the direct current source, the second means father including a first resistor coupled between the base terminal of the second transistor and the positive terminal of the direct current source.
 2. An ignition device as defined in claim 1, whereinthe second means further includes a third transistor having a second conductivity, the collector terminal thereof being coupled to the base terminal of the first transistor, and the emitter terminal thereof being coupled to a ground connection of the ignition device, and wherein the control stage is coupled to the base terminal of the third transistor to control the third transistor.
 3. An ignition device as defined in claim 2, whereinthe output stage further includes an electric current measuring device coupled to the primary winding and to the control stage for measuring the electric current flowing through the primary winding and for transmitting signals indicative thereof to the control stage.
 4. An ignition device as defined in claim 3, whereinthe current measuring device includes a second resistor coupled to the primary winding and to the control stage, the second resistor transmitting signals to the control stage indicative of the voltage drop across the primary winding.
 5. An ignition device as defined in claim 4, further comprising:a third resistor coupled between one terminal of the second resistor and an input terminal of the control stage, the third resistor exhibiting a higher resistivity than the second resistor; a fourth resistor coupled between the other terminal of the second resistor and another input terminal of the control stage, the fourth resistor exhibiting a higher resistivity than the second resistor; a first zener diode coupled between the third resistor and the respective input terminal of the control stage, and coupled to ground; and a second zener diode coupled between the fourth resistor and the respective input terminal of the control stage, and coupled to ground, the first and second zener diodes thus protecting the respective input terminals of the control stage.
 6. An ignition device as defined in claim 4, whereinthe control stage includes a fourth transistor; a diode, the anode terminal thereof being coupled to the emitter terminal of the fourth transistor, and the cathode terminal thereof being coupled to the base terminal of the first transistor and to a ground connection of the ignition device; and a fifth resistor coupled between the cathode terminal of the diode and the ground connection, the diode thus being provided to protect the control stage from voltage peaks across the primary winding.
 7. An ignition device as defined in claim 4, whereinthe second resistor is coupled between the emitter terminal of the first transistor and the ground-side terminal of the primary winding; and the ignition device further includesa fifth transistor, the emitter terminal thereof being coupled to the ground-side terminal of the primary winding, and the collector terminal thereof being coupled to the base terminal of the first transistor; and a voltage divider coupled between the emitter and collector terminals of the fifth transistor, wherein the base terminal of the fifth transistor is coupled to the pick-off thereof.
 8. An ignition device as defined in claim 1, whereinthe control stage, the output stage and the decoupling device are monolithically integrated. 